Common flat glass is called float glass because during the manufacturing process the glass floats on the top of a molten tin bath. The tin bath leaves small traces of metal or metal oxides on the surface of the glass that was in contact with the molten bath. Some glass processors that laminate or apply coatings to the glass require the knowledge of which side of the float glass was contacting the molten tin bath. This is especially important to glass processors when the coatings being applied have a reaction with the residue traces of metal or metal oxides, thereby changing the characteristics of the coating being applied.
Also, in the glass coating industry, there also are numerous applications where spectral reflective coatings are applied to a transparent surface. Some of these applications include flat glass, windows, LCD screens, solar cell panels, thermal efficient films, as well as many other plastic and glass applications. During the processing of these flat materials, it is often desirable to have an apparatus that is able to detect the presence and location of the “invisible” coatings. The coatings may be located on one or both surfaces of a single piece of transparent material, or on one or more surfaces of multiple pieces of transparent material built into an assembly, separated by a known transparent media such as a gas.
Also, in the building industry it is sometime necessary to identify if a completed product, such as a window, is made of a transparent glass having coating applied to a surface thereof.
The standard method of detecting the tin surface of glass is to cause the tin surface to fluoresce, resulting in a white visible glow that can be seen by human eyes. This test is performed by having the user place a UV light source close to the tin surface of the float glass. This method has been used for over 20 years and requires essentially three components: (1) a UV lamp, (2) an optical filter that passes the UV light but reflects the visible fluorescing light which helps viewing, and (3) the human eye which views the resulting glow. There have been no known improvements in this human eye method during the period of time.
Sensors have been added to the process to allow electronic inspection of the glow; for example, U.S. Pat. No. 4,323,785 describes discloses one method for detecting the presence and locations of transparent metallic oxides on glass sheets. This process uses ultraviolet lamps to cause the metallic oxide to fluorescence and the resulting glow is detected with sensors. This process requires large lamps, which generally must be mounted within an extremely close distance of the material under test.
Another device with a sensor utilizes a UV LED and a light sensor to sense the fluorescing glow. The results are indicated by illuminating an LED when placed on the tin surface of the glass.
In the past, users have had difficulty in obtaining a reading due to the unreliability of the prior devices. Such devices were difficult to use in most work/test environments due to the presence of ambient light in the work environment. In the past, it was generally understood that, during use of an apparatus for detecting a tin side of a glass, the user often needed to angle the apparatus away from the glass slightly and look under the apparatus in order to see whether there was a fluorescing glow from the tin side, or whether there was a lack of glow (non-tin side).
In order to be able to obtain an accurate reading, users sometimes placed their eye down close to the UV lamp, thus endangering their vision by exposure to UV light.
There is a continuing need for an improved, reliable and efficient method and device to accurately detect fluorescing material on various media using the human eye.
Therefore, it is desirable to have a surface coating detection apparatus that can be implemented that will easily show which surface has a coating and/or fluorescing material. It is also desirable to have a portable apparatus that can be used in the field by workers to quickly and accurately make such detections.